The diaphragms for pressure sensors are generally in the form of a very thin metal disk, for example a disk which is about 1/10-th of a millimeter thick. The periphery of the disk is intended to be housed, for example, in the body of the sensor. Under the effect of a difference in the pressures applied either side of the diaphragm, the diaphragm deforms and the resulting displacement of the center of the diaphragm is measured. This displacement measurement serves to deduce the value of the pressure difference.
Diaphragms in the form of a disk which is plane when at rest, are very flexible. In addition, the rest position of the center of such a diaphragm (i.e. when the pressures on either side of the diaphragm are equal) is relatively insensitive to temperature variations, to variations in the static pressure (i.e. the same pressure applied to both faces of the diaphragm) and to the force clamping the periphery of the diaphragm in the body of the sensor. Unfortunately, the linear zone of the curve representing displacement of the center of the diaphragm as a function of the differential of pressure which is applied thereto only corresponds to a relatively small range of displacements.
To remedy this lack of diaphragm response, it is well known to use corrugated type diaphragms. Such a diaphragm is described, for example, in published French patent No. 2 016 115. The thin sheet from which the diaphragm is made is shaped, e.g. by stamping, so as to have concentric corrugations around the center of the diaphragm, thus forming an alternating sequence of "ridges" and "furrows" from the periphery to the center. The diaphragm has circular symmetry about an axis which is perpendicular to its average plane. Because of the corrugations, the diaphragm has a displacement to differential pressure response which is substatially linear over a much wider range of displacements.
However, known corrugated diaphragms of circular symmetry have the drawback of being highly sensitive to temperature variations, to variations in static pressure and to the clamping of the periphery of the diaphragm in the body of the sensor. The effect of these spurious influences is particularly felt around the zero point of the sensor (i.e. the position of the center of the diaphragm when the differential pressure applied thereto is zero) and also on the sensitivity of the sensor.
Thus, when the temperature varies, or with variations in the clamping of the membrane in its housing, or when there are variations due to static pressure deformations, the periphery of the diaphragm is subjected to variations in radius which are imposed by relative deformation of the body (for example differential thermal expansion between the body of the sensor and the membrane).
These radius variations give rise to a variation in the sensitivity of the diaphragm both in the case of a diaphragm having circular corrugations about the axis of the diaphragm and in the case of a plane diaphragm. These variations in radius also cause a change in the position of the center of the diaphragm except when the diaphragm is plane by virtue of its perfect symmetry on either side of the plane in which the diaphragm is housed.
If the diaphragm is plane, the center does not move under the effect in variations of radius since the radial stresses which result therefrom are in the plane of symmetry of the diaphragm. In contrast, in circularly symmetrical corrugated diaphragms the housing plane is not a plane of symmetry and the center moves under the effect of the radial stresses. The resulting variations in the sensor zero point can be most disadvantageous in some applications.
To remedy this drawback of conventional corrugated diaphragms, the main object of the present invention is to provide a corrugated diaphragm which retains the advantages of conventional corrugated diaphragms, i.e. linear response over a wide range of displacements, but which has a zero point that is not sensitive to variations in temperature, static pressure or peripheral clamping force.